e9cec36348
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@51244 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
153 lines
4.1 KiB
TeX
153 lines
4.1 KiB
TeX
\section{\class{wxWeakRef<T>}}\label{wxweakref}
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wxWeakRef is a template class for weak references to wxWidgets objects,
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such as \helpref{wxEvtHandler}{wxevthandler}, \helpref{wxWindow}{wxwindow} and
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\helpref{wxObject}{wxobject}. A weak reference behaves much like an ordinary
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pointer, but when the object pointed is destroyed, the weak reference is
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automatically reset to a NULL pointer.
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wxWeakRef<T> can be used whenever one must keep a pointer to an object
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that one does not directly own, and that may be destroyed before the object
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holding the reference.
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wxWeakRef<T> is a small object and the mechanism behind it is fast
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(\textbf{O(1)}). So the overall cost of using it is small.
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\wxheading{Example}
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\begin{verbatim}
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wxWindow *wnd = new wxWindow( parent, wxID_ANY, "wxWindow" );
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wxWeakRef<wxWindow> wr = wnd;
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wxWindowRef wr2 = wnd; // Same as above, but using a typedef
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// Do things with window
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wnd->Show( true );
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// Weak ref is used like an ordinary pointer
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wr->Show( false );
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wnd->Destroy();
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// Now the weak ref has been reset, so we don't risk accessing
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// a dangling pointer:
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wxASSERT( wr==NULL );
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\end{verbatim}
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wxWeakRef<T> works for any objects that are derived from \helpref{wxTrackable}{wxtrackable}.
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By default, wxEvtHandler and wxWindow derive from wxTrackable. However,
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wxObject does not, so types like \helpref{wxFont}{wxfont} and
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\helpref{wxColour}{wxcolour} are not trackable. The example below shows how to
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create a wxObject derived class that is trackable:
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\begin{verbatim}
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class wxMyTrackableObject : public wxObject, public wxTrackable {
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// ... other members here
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};
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\end{verbatim}
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\wxheading{Predefined types}
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The following types of weak references are predefined:
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\begin{verbatim}
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typedef wxWeakRef<wxEvtHandler> wxEvtHandlerRef;
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typedef wxWeakRef<wxWindow> wxWindowRef;
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\end{verbatim}
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\wxheading{Derived from}
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wxTrackerNode
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\wxheading{Include files}
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<weakref.h>
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\wxheading{See also}
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\helpref{wxSharedPtr}{wxsharedptr}, \helpref{wxScopedPtr}{wxscopedptrtemplate}
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\wxheading{Data structures}
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{\small%
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\begin{verbatim}
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typedef T element_type
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\end{verbatim}
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}%
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\latexignore{\rtfignore{\wxheading{Members}}}
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\membersection{wxWeakRef<T>::wxWeakRef<T>}\label{wxweakrefwxweakref}
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\func{}{wxWeakRef<T>}{\param{T* }{pobj = NULL}}
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Constructor. The weak reference is initialized to {\it pobj}.
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\membersection{wxWeakRef<T>::\destruct{wxWeakRef<T>}}\label{wxweakrefdtor}
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\func{}{\destruct{wxWeakRef<T>}}{\void}
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Destructor.
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\membersection{wxWeakRef<T>::get}\label{wxweakrefget}
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\constfunc{T *}{get}{\void}
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Returns pointer to the tracked object or NULL.
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\membersection{wxWeakRef<T>::operator T*}\label{wxweakrefoperatorconvt}
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\constfunc{T*}{operator*}{\void}
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Implicit conversion to T*. Returns pointer to the tracked
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object or NULL.
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\membersection{wxWeakRef<T>::operator*}\label{wxweakrefoperatorreft}
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\constfunc{T \&}{operator*}{\void}
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Returns a reference to the tracked object. If the internal pointer is NULL
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this method will cause an assert in debug mode.
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\membersection{wxWeakRef<T>::operator->}\label{wxweakrefoperatorderef}
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\func{T*}{operator->}{\void}
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Smart pointer member access. Returns a pointer to the
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tracked object. If the internal pointer is NULL this
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method will cause an assert in debug mode.
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\membersection{wxWeakRef<T>::operator=}\label{wxweakrefoperatorassign}
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\func{T*}{operator=}{\param{T* }{pobj}}
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Releases the currently tracked object and starts tracking {\it pobj}.
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A weak reference may be reset by passing {\it NULL} as {\it pobj}.
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\membersection{wxWeakRef<T>::operator =}\label{wxweakrefoperatorassign2}
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\func{T*}{operator =}{\param{wxWeakRef<T>\& }{wr}}
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Release currently tracked object and start tracking the same object as
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the wxWeakRef {\it wr}.
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\membersection{wxWeakRef<T>::Release}\label{wxweakrefrelease}
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\func{void}{Release}{\void}
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Release currently tracked object and rests object reference.
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\membersection{wxWeakRef<T>::OnObjectDestroy}\label{wxweakrefonobjectdestroy}
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\func{virtual void}{OnObjectDestroy}{\void}
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Called when the tracked object is destroyed. Be default sets
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internal pointer to NULL.
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